> You can get
> things like
> signals for C++ with addon libraries,
> and you can
> get a type system for C++ with addon
> libraries.
> You can get named arguments as an
> addon too.

Yes, you can get them all from the same 'add-on library'. That's a language binding.

> But
> then it's not much different then
> coding with
> GTK+.

It's not too different. That's good. But it gives you less code, clearer code, and compile-time type-safety. That's good too.

> If a project for example uses
> GOB, it
> only uses GOB for those few classes it
> has. It
> does not emphasize subclassing for
> things it's not
> needed for.

I don't think it's an advantage that GTK+ in C makes subclassing difficult. Gtk-- in no way forces you to subclass, or emphasises that technique. That's just something that's available to you, whereas the difficulty of doing it in C means that people don't choose that design technique when they should. And code becomes less clear.

I guess GOB is meant to fix this. It's just that C++ seems like a nicer way to do that.

Convenient tool, but still only GTK+ expert could use it
In GTK+ widget writing, the most painful things I think are its
method/signal/argument definitions. At least 200-300 lines are
required to make a full featured GTK+ widgets. GOB makes it
easier. Good.

But you should already have experience writing GTK+ widgets
in plain C. Otherwise, you could not understand the errors from
the generated C codes by your C compiler.

And if the widget code is longer than (IMHO) 700-800 lines,
GOB does little help. In this case, its GTK+ OO overhead is
relatively small. And it might be better to write just in C, since
you can confused by GOB syntax while writing the big amount
of code in one .gob file

Back to the past
I'd just like to advice C users that there now exists a nice language called C++ that is really object oriented, and has all the power of C. At the beginning, it needed various sorts of preprocessors to be translated it to C, and then to be compiled. But now it is a real language, compiled as is. No need of curious things to make classes!
Check it out ;-)